Active Campaign offers personalization tags which dynamically pull in campaign data. By using combinations of these tags we can generate and pass unique identifiers (UUID) into the key parameter without the need for any javascript. For example:

%CAMPAIGNID%   pulls in your campaign’s unique ID
%MESSAGEID%   pulls in your campaign's unique message ID
%TODAY%
pulls in today's date
%CONTACTIP% pulls in the IP Address of the recipient

By combining these tags we can successfully create a dynamic UUID and our key parameter would therefore look something like this:
key=%CAMPAIGNID%|%MESSAGEID%|%TODAY%|%CONTACTIP%  

NOTE: the same UUID must always be passed into the key parameter of both the anchor and image tag

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